This invention relates to a tension shaft for machines for winding widths of sheet material, and more particularly to a tension shaft including a central shaft having an outside diameter which may be altered by air fed into or withdrawn from a flexible tube wound thereabout.
In an adjustable tension shaft assembly for a winding frame, the frame becomes firmly coupled to the tension shaft upon increasing the diameter of the shaft. It is known to alter the outside diameter by inflating a flexible tube on the outer surface of the tension shaft. For example, in a known tension shaft of this type as disclosed in German Pat. No. 2,655,935, several tube units are uniformly distributed over the periphery and extend parallel to each other in the longitudinal direction of the tension shaft. Air is fed into the tubes by means of a central valve arranged at one end of the shaft and a connecting central hole with radial channels running into the different hose elements.
An inlet is provided as a transition between the radial holes and the individual tube part. The inlet is formed by a plate with a central support projecting into the radial channel. The plate lies inside the tube and the support is kept firmly in the radial channel by clamp elements. This construction generally does not withstand the centrifugal forces which arise at high rotation rates. Plates clamped with pegs tend to loosen at appropriate loads which leads to rendering the tension shaft unsuitable for further use. In addition, mounting of the conventional air inlets is relatively costly. Finally, the plate, which must be applied tightly to the inside of the tube area, must be designed in a relatively large size in order to provide sufficient tightness which is obtainable only with a plate of large surface area. Additionally, the assembly cost for replacing such a tube, which is necessary after a certain operating time, is also relatively costly.
In another known solution described in German Application No. 8,004,622, a tube is wound in spiral fashion about a central shaft piece. In this construction, the tube is placed on a central valve provided on one side of the shaft and is fastened with a clamp. The tube is also slightly bent as it emerges to the outside of the central shaft piece. This tends to cause disturbances in the air currents or tends to rupture the tube at the location of this transition to the end of the central shaft piece. Similarly, in the case of wear of the valve and/or the tube, replacement of the worn part is only possible by extensive assembly work.
Accordingly, it would be desirable to provide a tension shaft having an adjustable outside diameter so as to provide a simple and wear-resistant assembly including a flexible tension tube having an air inlet and valve which may be also readily assembled or disassembled.